The technologies related to fiber-reinforced composite materials have made marked progress. As for the resin matrices alone, not only thermosetting resins such as epoxy resin, unsaturated polyester resin, and phenol resin but also thermoplastic resins such as polypropylene, polyamide, and polyethylene terephthalate are widely used. As to the reinforcing fibers, on the other hand, various fibers are studied and produced including glass fiber, and also carbon fiber, aramid fiber, alumina fiber, silicon carbide fiber, and whisker.
It has been attracting attention in recent years that an aromatic polyester which exhibits anisotropy in its molten state can provide a light weight fiber of high strength and high modulus of elasticity in a rational process of melt spinning, which uses no solvent and gives low loss of materials.
In the present state of art, however, when the said aromatic polyester fiber is used in a composite material with a resin, even though the properties of the fiber itself are excellent, the resulting composite material cannot make the most of the excellent properties because of poor adhesion between the fiber and the resin and poor dispersion of the fiber in the resin.